In a compressor of a turbocharger that supplies compressed air to an engine, a surge may occur in a case where a flow rate is low relative to a pressure ratio between an inlet and an outlet. The surge of the compressor is an abnormal operation state of the compressor which occurs in a case where a flow rate is low relative to a pressure ratio. When the surge occurs, vibration of the flow rate or the pressure is caused due to flow separation or reattachment.
If the surge continues, the compressor is likely to be damaged. Accordingly, measures are taken to avoid the surge. For example, measures are taken such as selecting a compressor having a margin so that an operating point does not enter a surge area, and avoiding the surge by means of a logic using a map (parameter) indicating characteristics of the compressor.
However, even in a case where measures are taken to avoid the surge, characteristics of the compressor are likely to change due to aging or the like and a surge is likely to occur. Therefore, a technology for determining whether or not there is a surge has been proposed.
For example, PTL 1 discloses that a temperature detection device that detects a temperature of a gas passing through an intermediate cooler arranged between a plurality of compression stages and flowing into a next-stage compressor is provided, and a turbo compressor performs a determination as to a surge on the basis of the temperature detected by the temperature detection device.